Nebulae are enormous clouds of gas (“nebula” is Latin for cloud). Our Milky Way Galaxy is permeated with gas, most of it hydrogen and helium, which is concentrated in its spiral arms. In most cases, this gas can form into dense nebulae. If they are illuminated by nearby stars, nebulae shine brightly and appear as wispy clouds when seen through a telescope; if unilluminated, they appear as blotches of darkness silhouetted against the background stars. There is no difference between a dark nebula and a bright one, except for the lack of illumination.
Dark nebulae (or absorption nebulae) can be enjoyed with the unaided eye, with binoculars and rich-field telescopes (RFTs), or with the largest amateur instruments. They range from small black voids a few arcminutes across to the Great Rift of Cygnus, stretching more than 120° from Deneb to Alpha Centauri.
Few dark nebulae are as prominent as the Great Rift, however. Most are subtle contrast features winding through the richest star clouds. A perfect example is the 7°-long Pipe Nebula, a beautiful naked eye object in southern Ophiuchus.
Start your search about 10° east of Antares. Look for a line of three stars of magnitudes +3 and +4, the only prominent stars in that area of sky. The brightest, Theta Ophiuchi, lies at the line’s midpoint and the bowl of the Pipe Nebula is centered 3° southeast of Theta. The bowl, designated Barnard 78, appears as a jagged rectangular formation, with an opacity of 5. In a 1 to 6 scale, the most opaque dark nebulae are classed opacity 6, and the least opaque as opacity 1.
The pipe’s stem is formed from Barnard 59, 65, 66, and 67. It extends for over 5° to the west from the base of the bowl. With the unaided eye, the stem looks like a nearly straight dark cloud. The subtle details come to light when viewed through binoculars, only if the skies are especially clear.
Finder map – field width 25°, stars to magnitude +7.